Catalysis

“ It is convenient to divide catalytic actions into two groups:— (1) when the catalyst first combines with one of the reaction components to form a compound which immediately reacts with the other components, the catalyst being simultaneously liberated, and free to react with more of the undecomposed first component; and (2) , when the catalyst apparently reacts by mere contact. The theory of catalysis is treated under Chemical Action ”

“ A catalyzer is a substance which changes the velocity of a reaction, but does not change its products.
Examples of Catalysis. We have already had several instances of such action. Oxygen and hydrogen combine with each other at ordinary temperatures in the presence of platinum powder, while if no catalytic agent is present they do not combine in appreciable quantities until a rather high temperature is reached. Potassium chlorate, when heated with manganese dioxide, gives up its oxygen at a much lower temperature than when heated alone. ”

“ It is probable that many of the chemical transformations in physiological processes, such as digestion, are assisted by certain substances acting as catalytic agents. The principle of catalysis is therefore very important. ”

“ A true theory of catalysis will enable us to solve the problem of the transmutation of the elements, of which we have already had examples in the substances derived from radium, and the recent derivation of tellurium from copper by Sir William Ramsay. The action of animal and vegetable protoplasm is probably catalytic and the chemist can now make some vegetable substances, such as indigo or alizarine, more cheaply and purely than the plants themselves do. ”

“ This liberation of large quantities of potential energy by an exceedingly small external stimulus has not hitherto received the consideration it demands. Certain phenomena, such as those of chemical catalysis or the action of soluble ferments, excite our astonishment because such extremely small quantities of {106}certain substances will determine the chemical transformations of large quantities of matter, there being no proportion between the amount of the catalytic substance and of the matter transformed. ”

“ Acids and bases appear to act catalytically upon all reactions involving consumption or liberation of water, and indeed that action is proportional to the concentration of the hydrogen or hydroxyl-ions. Further, the decomposition of hydrogen peroxide is “catalysed” by iodine-ions, the condensation of two molecules of benzaldehyde to benzoin by cyanogen-ions. One of the earliest known and technically most important instances of catalysis is that of the oxidation of sulphur dioxide to sulphuric acid by oxygen in the presence of oxides of nitrogen. ”

“ Subsequent work has shown that other organisms act by the enzymes they contain, so that it is now recognized that there is no essential difference between the living or organized ferment and the non-living or unorganized ferment. All ferments probably act as catalysators or catalysts. Catalysis is the process by which reactions are either initiated or accelerated by the mere presence of certain substances which remain unchanged during the process ”

“ Outside the animal body, the customary components of our daily food, the proteins, fats and carbohydrates, are not affected by oxygen even at the body temperature or by long exposure to the gas. Catalytic action is a necessary prelude to their oxidation, and it is the smaller molecules resulting from the action of enzymes working through catalysis that are mainly burned up or broken down with liberation of their contained energy. ”

“ A species of lead from Ceylon, whose atomic weight is slightly different from that of ordinary lead, lends colour to these assertions, though it cannot be supposed that all the lead in nature is derived from radio-active metals of higher atomic weight.
The subject of catalysis is assuming a greater commercial importance than heretofore, it having been discovered that hydrocarbons are enabled by this means to take up additional atoms of hydrogen, and form oils, while certain oils can be hardened into fats. ”

“ While the chemist, on the other hand, recognises it as a familiar phenomenon, and refers it to the same category as his other known examples of autocatalysis. {132}
This very important, and perhaps even fundamental phenomenon of growth would seem to have been first recognised by Professor Chodat of Geneva, as we are told by his pupil Monnier168. “On peut bien, ainsi que M. Chodat l’a proposé, considérer l’accroissement comme une réaction chimique complexe, dans laquelle le catalysateur est la cellule vivante, et les corps en présence sont l’eau, les sels, et l’acide carbonique.” ”

“ After a moment: "Naturally, this combination decreases the total volume of gas; so the pump has to pull in more hydrogen from outside to satisfy its barystat, and more nitrogen is welling from below all the time. We've been operating quite an efficient little ammonia factory down there, though it should reach equilibrium as to pressure and yield pretty soon.
"The Haber process catalyst, incidentally, is spongy iron with certain promoters—potassium and aluminum oxides are excellent ones. ”

“ Bayliss defines enzymes as the “catalysts produced by living organisms.” A catalyst is a body which greatly accelerates the rate of reaction in chemical processes, without apparently taking part in the process. For instance, peroxide of hydrogen is decomposed into oxygen and water by mere contact with finely divided platinum, while the latter remains unaltered in the process. ”

“ This is the case with many of the organic compounds of carbon and hydrogen.
The elements of a compound may be disassociated, and thus the dissimilar substances of which it is composed set free. A piece of chalk exposed to heat is, by the disturbance of its molecular arrangement, changed in its nature; a gaseous body, carbonic acid, is liberated, and quick-lime (oxide of calcium) is left behind. If this carbonic acid is passed through red-hot metal tubes, or brought in contact with heated potassium, it is resolved into oxygen and charcoal—the oxygen combining with the metal employed. ”

“ Thus we learn that chalk is a body consisting of two compound molecules,—carbonic acid, which is formed by the combination of an atom of carbon with two atoms of oxygen,—and lime, which results from the union of an atom of calcium with one of oxygen.
The condition requisite to the production of chemical action between bodies is that they should be dissimilar. Two elementary atoms are placed within the spheres of each other’s influences, and a compound molecule results. Oxygen and hydrogen form water; oxygen and carbon give rise to carbonic acid; nitrogen and hydrogen unite to form ammonia ”

“ The discovery of catalytic agents is, as a rule, the result of accident. I do not think that any guide exists which would enable us to predict that any particular substance would cause an acceleration or a retardation of any particular reaction. But catalytic agents are generally those which themselves, by their power of combining with or parting with oxygen, or some other element, cause the transfer of that element to other compounds to take place with increased or diminished velocity. ”

“ A crystal is a mass of molecules, all of the same composition. A molecule in its turn is made up of atoms, and each atom is a unit mass of an element. Thus the calcite molecule is made up of one unit or atom of calcium, one of carbon, and three 12 of oxygen (CaCO3) . These atoms are held together by an attraction, and make a molecule, and for the study of minerals the molecule is the unit. The mineral, calcite, is a mass of molecules all like the one above, and each molecule so small as to be invisible even with the aid of the most powerful microscope. ”

“ The reason is that the capacity of ordinary matter for stopping the rays varies approximately as the fourth power of the atomic number of the elements concerned. Thus carbon, whose atomic number is 6, is 1296 times as effective as hydrogen in stopping X-rays; oxygen, whose atomic number is 8, is 4096 times as effective as hydrogen; nitrogen, whose atomic number is 7, is 2401 times as effective as hydrogen; calcium, whose atomic number is 20, is 160,000 as effective as hydrogen. The human body consists mainly of carbon, oxygen, nitrogen and hydrogen, but the bones consist mainly of calcium. ”

“ Thus, one atom of nitrogen unites with three of hydrogen, one of carbon with four of hydrogen, and so on. Every substance has, therefore, what is called its ‘quantivalence,’ or power of uniting with it a greater or less quantity of other atoms, and conversely that of replacing in combinations other atoms, or groups of atoms, the sum of whose quantivalence equals its own. Thus, one atom of carbon, which has four poles, combines with four atoms of hydrogen or chlorine, which is unipolar, but with only two of oxygen, which are bipolar ”

“ For that reason the catalyst is referred to as "a chemical parson." Finely divided metals have a strong catalytic action. Platinum sponge is excellent but too expensive. So in this case nickel is used. A nickel salt mixed with charcoal or pumice is reduced to the metallic state by heating in a current of hydrogen. Then it is dropped into the tank of oil and hydrogen gas is blown through. The hydrogen may be obtained by splitting water into its two components, hydrogen and [Pg 205] oxygen, by means of the electrical current, or by passing steam over spongy iron which takes out the oxygen. ”

“ In a mechanical mixture, as we have seen, the elements which are to react one upon another are brought together in separate bodies. In gunpowder, for example, the carbon is contained in the charcoal, and the oxygen in the saltpetre. But in a chemical compound, these elements are brought together in the same body. In a mechanical mixture, we may put what proportion of oxygen we please. But elements combine chemically only in certain definite proportions, so that in the chemical compound we can introduce only a certain definite proportion of oxygen. ”

“ It is evident, that a constant value is found for the ratio [H+] × [CH3CO2−] / [CH3CO2H] and that the ionization of acetic acid, in these dilute solutions, obeys the law of chemical equilibrium.181 The equilibrium constant expresses in definite, quantitative terms the tendency of acetic acid to ionize in dilute solution. Examination of other acids shows that there is an enormous range in the values found for their respective ionization constants. The constants are the best measure of the strength of the acids as acids. ”

“ Hitherto I have spoken of chemical decomposition only as produced by motion, and heat, and light, but now I must give a familiar instance in which you can produce great chemical change and movement amongst atoms by simply mixing two chemicals together. Add tartaric acid to a solution of carbonate of soda and a great commotion ensues, owing to the superior affinity of the tartaric acid for the soda; and which acid displaces the carbonic acid in previous union with the soda, and the latter acid is turned out and escapes by violent effervescence. ”

“ If brought into contact with a solution of some substance which will withdraw the hydroxyl ions, converting them into water, or into some non-ionized substance, they are replaced at the expense of the molecules of non-ionized ammonium hydroxide; and these, when diminished in amount, draw on the store of molecules of ammonia and water, which combine, so as to maintain equilibrium, Now the investigation of such changes must belong to the domain of inorganic chemistry. It is true that the methods of investigation are borrowed from the physical chemist ”

“ The power of affinity reciprocally exerted by the hydrogen, charcoal, and oxygen, in these acids, is in a state [Pg 121] of equilibrium only capable of existing in the ordinary temperature of the atmosphere; for, when they are heated but a very little above the temperature of boiling water, this equilibrium is destroyed, part of the oxygen and hydrogen unite, and form water; part of the charcoal and hydrogen combine into oil; part of the charcoal and oxygen unite to form carbonic acid ”

“ Rogers, catalysts. Catalysts is the name of a chemical reaction consisting essentially of a decomposition and a new combination effected by means of a catalyst which acts on the compound bodies in question, but which goes through the reaction itself unchanged. There are a great many of them which are used in the arts and in manufacturing, and while their action is not always clearly understood, the results are well known and can be banked on. ”

“ When the pressure of the carbon dioxide reaches a certain value (which is found to depend on the temperature) , decomposition ceases, and calcium carbonate exists side by side with calcium oxide and carbon dioxide. Moreover, at any given temperature the pressure is constant and independent of the amount of carbonate or oxide present, or of the volume of the gas; nor does the addition of either of the products of dissociation, carbon dioxide or calcium oxide, cause any change in the equilibrium. ”

“ A. A. Noyes describes a similar experiment with sodium chloride and silver nitrate, loc. cit.
CHAPTER VIII SIMULTANEOUS CHEMICAL AND PHYSICAL EQUILIBRIUM.—THE SOLUBILITY- OR ION-PRODUCT.
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It frequently happens that we have to deal, simultaneously, with conditions of chemical and of physical equilibrium, obtaining in the same system. For instance, a gas like carbon dioxide, in contact with its saturated solution in water, is in equilibrium with the dissolved carbon dioxide, and this, in turn, is in equilibrium with its hydrate, carbonic acid. ”